1. Field of the Invention
The present invention relates to an apparatus and a method for conditioning the polishing surface of a polishing pad with high precision.
2. Related Background Art
With the recent progress in the ultra fine geometry and in the multi-layered wiring of the semiconductor devices, there is being required high precision polishing apparatuses for flattening the surface of a substrate such as semiconductor wafer for example of Si, GaAs, InP or SOI, with high precision. Among such apparatuses, there is known a chemical mechanical polishing (CMP) apparatus for flattening the surface of a substrate such as a wafer on which the semiconductor devices are formed, with high precision.
The CMP apparatuses can be divided into two types as shown in FIGS. 1 and 2.
(1) FIG. 1 is a schematic view of a polishing part of a CMP apparatus for executing the polishing operation in the state of facing the surface to be polished of a wafer 100 downwards.
As shown in FIG. 1, the wafer 100 is supported by a wafer chuck 400 in the state of facing the polished surface downwards and is pressed, in the state of rotation of the wafer (Hereinafter, "rotation" means the action of an object of turning on its own axis.), to a polishing pad 200 of a diameter larger than that of the wafer 100 to thereby polish the wafer. In the polishing operation, a polishing agent (slurry) 300 is supplied by dripping onto the upper surface of the polishing pad 200.
The wafer chuck 400 supports the wafer 100 by attachment utilizing, for example, vacuum suction, wax, solution or deionized water, and a guide ring (not shown in the drawings) may be provided along the periphery of the wafer 100 in order to prevent displacement thereof. The diameter of the polishing pad 200 on a polishing table 500 is 3 to 5 times that of the wafer 100, and the slurry consists of a suspension of finely powdered silicon oxide mixed in the aqueous solution of potassium hydroxide.
As shown in FIG. 1, the CMP apparatus is further provided with conditioning means 600. The conditioning means 600 has an annular shape with a diameter smaller than that of the polishing pad 200, and is maintained in contact with a part of the polishing pad 200. The conditioning means 600 moves on the polishing pad 200 while executing a rubbing movement such as rotation or swinging, thereby removing the particles of the slurry and the polished wastes generated in the polishing operation from the entire surface of the polishing pad 200.
There is also proposed, as illustrated in FIG. 2, a method of supporting a wafer 100 in the state of facing the surface to be polished upwards by a wafer chuck 800 provided on a wafer table 700 and having a guide ring (not shown in the drawings) and then polishing the wafer 100 with a polishing pad 900 of a diameter smaller than that of the wafer 100.
Such polishing apparatus and method are suitable for polishing the currently employed semiconductor wafers of 8 inches in diameter, but it is said that the wafers are shifted from 8 inches to 12 inches in the near future, following the continuing progress in the semiconductor technology toward the finer geometry of the integrated circuits and the larger diameter of wafer.
For polishing the wafer of a large diameter, the above-described technology is associated with the following technical problems.
In the above-described polishing apparatus, in polishing the 8-inch wafer, the polishing performance is adjusted by optimizing the thickness and elasticity of the polishing pad, but it is difficult to achieve delicate adjustment or to maintain uniformity in the material of the polishing pad, so that high-quality polishing is difficult to attain in the wafer of a larger diameter such as 12 inches.
For example, in case of employing a polishing pad of a diameter smaller than that of the wafer as described in the foregoing, it is difficult to obtain a uniform polishing amount over the entire surface of the wafer. Also there is required a long polishing time in case of polishing the entire surface of the wafer with a polishing pad of a diameter smaller than that of the wafer. Also in case of polishing the entire wafer with a polishing pad of a diameter larger than twice that of the wafer, the polishing amount becomes larger in the central area of the polishing pad than in the peripheral area of the polishing pad, because of the circumferential speed between the central area of rotation of the polishing pad and the peripheral area thereof, so that it is difficult to control the polishing amount. Also, since the rotation of the polishing pad is executed while only a part of the polishing pad is in contact with the wafer, it may be degraded, abraded or even deformed in a donut shape. Furthermore, the polishing pad may be deformed by the pressure applied thereto during the wafer polishing. All these phenomena cause the degradation of the uniformity of polishing and the flatness by the polishing.
Also in case of polishing the surface of a wafer to be polished facing downwards by the polishing pad of a diameter larger than twice that of the wafer as described in the foregoing, the polishing agent is supplied not only to the area of the polishing pad in contact with the wafer but also to the entire surface of the polishing pad. For this reason, there is consumed a large amount of the polishing agent, thereby leading to a higher cost.
Also in the above-described polishing apparatus, it is difficult to achieve uniform conditioning over the entire surface of the polishing pad with the conditioning means. This is because the conditioning means is in contact with only a part of the polishing pad. More specifically, the polishing pad is deformed at the boundary of an area in contact with the conditioning means and an area not in contact therewith, and this causes generation of uneven conditioning in such deformed part.
As explained above, the above-described conditioning technology results, within the conditioned polishing pad, in an area sufficiently conditioned having a high polishing ability and an area not sufficiently conditioned.
It is difficult to uniformly polish the substance to be polished such as a wafer by using the polishing pad showing such unevenness.
Also in case of employing the conditioning means with an area smaller than that of the polishing pad, there is required a long time for conditioning the entire surface of the polishing pad.